Assuming a firearm, that is configured to use a lower and upper receiver configuration, is in sound working condition, it is common knowledge for those skilled in the art that the rear connection points of the lower receiver (the “rear coupler” hereafter) and of the upper receiver (the “rear knuckle” hereafter) will cooperate with each other and may be axially-engaged by a takedown pin to secure the rear connection points of the receivers. By “axial-engaged” is meant that the pin is inserted axially through axial pin-hole(s) in each of the rear coupler and the rear knuckle. Furthermore, when the lower and upper receivers' rear connection points are securely axially-engaged and coupled together, the breach of the firearm is also known to be in a closed and operable position because the trigger hammer and the firing pin are in alignment. In this closed and operable position, the firearm can be properly discharged, when the trigger is depressed to cause the trigger hammer to strike the firing pin, which then strikes the primer of the round to discharge the round from the firearm.
Conversely, when the takedown pin is installed to the lower receiver, but axially-disengaged from the upper receiver, the upper and lower receivers are no longer securely connected at their rear connection points, and, thus, the receivers are allowed to separate at their rear connection points by pivoting on their forward pivot pin hinge. “Axially-disengaged” means axially inserted only to an extent that the pin extends into one (the proximal) sidewall of the lower receiver, and so into only one of the rear coupler pin holes, and not through the rear knuckle of the upper receiver. Thus, when the receivers are separated at their rear connection points enough to misalign the trigger hammer and the firing pin, they can no longer interact together and the firearm is considered to be in an inoperable mode. Furthermore, when the receivers are allowed to substantially pivot open and separate at their rear connection points, the internal bodies of the receivers and the components assembled within the receivers are accessible for cleaning, maintenance, and/or replacement. Thus, the takedown pin is an integral part of the overall configuration, safety, maintenance, and operation of a firearm using this type of lower and upper receiver configuration.
The takedown pin is conventionally a component of a “takedown pin assembly” that comprises the takedown pin and a detent-pin system (including a detent spring, and a detent pin received in a detent pin hole in the lower receiver). These components may be assembled/installed in both the lower and upper receiver, to create the beneficial connection and/or disconnection of the receiver's rear connection points as discussed above. Alternatively, the takedown pin assembly may be assembled/installed only in the lower receiver, without connection of the upper receiver, that is, without the pin being installed in the upper receiver pin hole. This installation only in the lower receiver may be done for storage of the lower receiver and takedown pin assembly as a unit, and/or prior to a later step of connecting the upper receiver. This is possible because the takedown pin assembly, by virtue of the detent system, may be pushed or pulled into, and temporarily held in, either the axially-disengaged position extending only into one sidewall portion of the rear coupler, or the axially-engaged position extending into both sidewall portions of the rear coupler, whether or not the upper receiver is connected by its rear knuckle being inserted into the rear coupler of the lower receiver and then being captured by the takedown pin. Therefore, at certain times, the operator will install the pin of a conventional takedown pin assembly in the lower receiver, in either the axially-disengaged position or the axially-engaged position, without the upper receiver being connected. For subsequent connection of the upper receiver, the operator simply maintains the takedown pin in, or axially pulls the takedown pin back to, the axially-disengaged position, inserts the upper receiver's rear knuckle into the rear coupler of the lower receiver, and then pushes the takedown pin to the axially-engaged position to complete the takedown pin assembly and connection of the upper and lower receivers. Therefore, one may describe the takedown pin assembly as being “assembled to” or “installed in” the lower receiver in certain cases, and as being, “assembled to” or “installed in” the lower receiver and upper receiver in other cases.
Considering the configurations, components, and methods of use for the takedown pin, lower receiver, and upper receiver, it is also important to consider their influence on the firearm's breach and its subsequent effect on the alignment and operation of the trigger hammer and firing pin of the firearm, as discussed above. For those familiar with firearms that are configured to use a lower and upper receiver and that are also properly assembled and in sound working condition, one may assume that, when the takedown pin is axially-engaged into the lower and upper receivers, the lower and upper receivers are securely coupled at their rear connection points, and, therefore, the breach of the firearm is in an operable mode because the trigger hammer and firing pin are in alignment and in position to discharge the waiting round. Conversely, when the takedown pin is axially-disengaged from the upper receiver and the receivers have been separated at their rear connection points, the breach of the firearm is in an inoperable mode as the trigger hammer and firing pin are no longer in alignment and/or able to interact; this inoperability due to lack of hammer and pin alignment may occur even if the rear connection points of the lower and upper receivers are only slightly separated. Conventional takedown pin, lower receiver, and upper receiver configurations, and methods of placing them into an inoperable position, are problematic, as they typically require the takedown pin to be axially-disengaged either partially or completely from the upper receiver in-order to allow the receivers to separate at their rear connection points, and this may be considered by operators to be an unsafe, cumbersome and/or tedious process to perform.
Further, axially-disengaging and/or engaging the takedown pin from and/or to the upper receiver may be inefficient, difficult, take excess time, and/or require excessive force to perform. In addition, when the takedown pin is disengaged from the upper receiver, thus allowing the lower and upper receivers to freely separate and pivot on the forward pivot pin hinge, it may be difficult and/or awkward for the operator to control the pivoting movements of the receivers. This difficulty or awkwardness may occur especially when the operator is trying to perform critical tasks, such as engaging and/or disengaging the magazine of the firearm while the breach of the firearm is in an open and inoperable position, which may be desired and/or necessary for some operators and/or firearm configurations.
As mentioned above, there are operators who desire and/or require the breach of certain firearm embodiments to be open and placed into an inoperable mode, in-order to perform critical tasks like engaging and/or disengaging the magazine to and/or from the firearm. When tasks like this are performed, it is important the operator of the firearm can perform the tasks needed in a safe and controlled manner, which may be hindered by: 1) the conventional process of axially-engaging and/or axially-disengaging the takedown pin from the upper receiver, and 2) the resulting potential of uncontrolled and awkward pivoting movements of the firearm when the rear connection points of the lower and upper receivers are no longer being controlled by the takedown pin.
Furthermore, these concerns regarding conventional takedown pins and receivers are more likely and/or more serious when the processes are performed under stressful and/or adverse conditions, which is likely the case when performed by military, law enforcement or other operators needing to perform these tasks in the field. Thus, there is a need to improve and/or simplify the conventional process of securing, semi-securing, and/or unsecuring the rear connection points of the lower and upper receivers. Embodiments of the invention meet one or more of these needs, as will be further understood from the following disclosure and discussion.